1. Field of the Invention
This invention relates to microcell electrochemical devices and assemblies, methods of making same by various techniques, and use of such devices and assemblies.
2. Description of the Art
In the field of energy supplies and energy conversion devices, and particularly in the development of fuel cells and batteries, there has been continuing effort to develop devices with significant power outputs (high current and/or high voltage), high power density, and high energy output per unit volume.
Structurally, electrochemical cells such as batteries and fuel cells are relatively simple, utilizing respective positive and negative electrodes separated in such manner as to avoid internal short circuiting, and with the electrodes being arranged in contact with an electrolyte medium. By chemical reaction at the electrodes, the chemical energy of the reaction is converted into electrical energy with the flow of electrons providing power when the electrode circuit is coupled with an external load.
Battery cells may use separator plates between respective electrodes so that multiple sheet elements are arranged in successive face-to-face assemblies, and/or such sheets may be wound together in a (spiral) roll configuration.
The fuel cell is of significant current interest as a source of power for electrically powered vehicles, as well in distributed power generation applications.
In fuel cells, a fuel is introduced to contact with an electrode (anode) and oxidant is contacted with the other electrode (cathode) to establish a flow of positive and negative ions and generate a flow of electrons when an external load is coupled to the cell. The current output is controlled by a number of factors, including the catalyst (e.g., platinum in the case of hydrogen fuel cells) that is impregnated in the electrodes, as well as the kinetics of the particular fuel/oxidant electrochemical reaction.
Currently, single cell voltages for most fuel cells are in the range of about 0.6-0.8 volts. The operating voltage depends on the current; as current density increases, the voltage and cell efficiency correspondingly decline. At higher current densities, significant potential energy is converted to heat, thereby reducing the electrical energy of the cell.
Fuel cells also may be integrated with reformers, to provide an arrangement in which the reformer generates fuel such as hydrogen from natural gas, methanol or other feed stocks. The resulting fuel product from the reformer then is used in the fuel cell to generate electrical energy.
Numerous types of fuel cells have been described in the art. These include:
polymer electrolyte fuel cells, in which the electrolyte is a fluorinated sulfonic acid polymer or similar polymeric material;
alkaline fuel cells, using an electrolyte such as potassium hydroxide, in which the KOH electrolyte is retained in a matrix between electrodes including catalysts such as nickel, silver, metal oxide, spinel or noble metal;
phosphoric acid fuel cells using concentrated phosphoric acid as the electrolyte in high temperature operation;
molten salt fuel cells employing an electrolyte of alkali carbonates or sodium/potassium, in a ceramic matrix of lithium aluminate, operating at temperatures on the order of 600-700 degrees C., with the alkali electrolyte forming a high conductive molten salt;
solid oxide fuel cells utilizing metal oxides such as yttria-stabilized zirconia as the electrolyte and operating at high temperature to facilitate ionic conduction of oxygen between a cobalt-zirconia or nickel-zirconia anode, and a strontium-doped lanthanum manganate cathode.
Fuel cells exhibit relatively high efficiency and produce only low levels of gaseous/solid emissions. As a result of these characteristics, there is great current interest in them as energy conversion devices. Conventional fuel cell plants have efficiencies typically in the range of 40-55 percent based on the lower heating value (LHV) of the fuel that is used.
In addition to low environmental emissions, fuel cells operate at constant temperature, and heat from the electrochemical reaction is available for cogeneration applications, to increase overall efficiency. The efficiency of a fuel cell is substantially size-independent, and fuel cell designs thus are scalable over a wide range of electrical outputs, ranging from watts to megawatts.
A recent innovation in the electrochemical energy field is the development of microcellsxe2x80x94small-sized electrochemical cells for battery, fuel cell and other electrochemical device applications. The microcell technology is described in U.S. Pat. Nos. 5,916,514; 5,928,808; 5,989,300; and 6,004,691, all to Ray R. Eshraghi. The microcell structure described in these patents comprises hollow fiber structures with which electrochemical cell components are associated.
The aforementioned Eshraghi patents describe an electrochemical cell structure in which the single cell is formed of a fiber containing an electrode or active material thereof, a porous membrane separator, electrolyte and a second electrode or active material thereof. Cell designs are described in the Eshraghi patents in which adjacent single fibers are utilized, one containing an electrode or active material thereof, the separator and electrolyte, with the second fiber comprising a second electrode, whereby the adjacent fibers constitute positive and negative electrodes of a cell.
The present invention embodies additional advances in the Eshraghi microcell technology.
The present invention relates to series-connected microcell electrochemical devices and assemblies, and methods of making and using the same.
In one aspect, the invention relates to a microcell assembly, wherein each microcell comprises:
an inner electrode,
a microporous membrane separator in contact with the inner electrode,
an electrolyte in pores of the microporous membrane separator,
an outer electrode,
such assembly comprising a first cell including a first microcell sheet member comprising a plurality of microcell fibers parallely arranged and interconnected in a substantially planar conformation, with inner current collectors of the microcell fibers axially extending from a first edge of a first sheet member, and a second sheet member of external current collectors overlying the first sheet member, with each current collector in contact with at least one microcell fiber of the first sheet member and extending beyond an opposite, second edge of the first sheet member;
an insulating sheet for electrical isolation of the first cell from a further cell overlying the insulating sheet;
a second cell including a first microcell sheet member comprising a plurality of microcell fibers parallely arranged and interconnected. in a substantially planar conformation, with inner current collectors of the microcell fibers axially extending from one edge of the second sheet member, adjacent the second edge of the first sheet member, and a second sheet member of external current collectors overlying the first sheet member, with each current collector in contact with at least one microcell fiber of the first sheet member and extending beyond the opposite edge of the first sheet member;
wherein the inner current collectors of the first cell are aligned with and electrically connected to the outer current collectors of the second cell to form a series connection therewith.
Another aspect of the invention relates to a microcell module, comprising:
a gas feed chamber including a perforate plate member;
a microcell assembly as described hereinabove, positioned on the perforate plate member, and potted at respective ends thereof by potting members forming respective seal faces which when the seal faces at their periphery are abuttingly reposed in a housing, form a shell and tube structural arrangement, wherein the perforate plate member is intermediately positioned between the potting members.
A still further aspect of the invention relates to a microcell sub-bundle article, comprising:
a sheet assembly including a first microcell sheet member comprising a plurality of microcell fibers parallely arranged and interconnected in a substantially planar conformation, with inner current collectors of said microcell fibers axially extending from a first edge of a first sheet member, and a second sheet member of external current collectors overlying the first sheet member, with each current collector in contact with at least one microcell fiber of the first sheet member and extending beyond an opposite, second edge of the first sheet member;
wherein the sub-bundle has been formed by axially rolling the sheet assembly into a cylindrical pre-form, applying a porous and electrically insulative wrap to the outer cylindrical surface of the cylindrical pre-form; and potting at respective ends of the cylindrical pre-form, to yield the sub-bundle,
wherein the first and second sheet members form a cell.
Another aspect of the invention relates to a microcell article comprising a series of microcell sub-bundle articles, sequentially connected in positive-to-negative electrode arrangement, in a bundle wherein component sub-bundle articles are parallelly aligned with one another in side-by-side relationship of consecutive sub-bundle articles, and the bundle has an axial dimension that substantially equal to the axial dimension of each sub-bundle article in the bundle.
A further aspect of the invention relates to a microcell article, comprising a plurality of microcell sub-bundle articles, arranged in side-by-side relationship, with electrodes of adjacent ones of the sub-bundle articles being electrically interconnected in positive-to-negative electrode relationship, and with the microcell article being potted at respective ends thereof.
Yet another aspect of the invention relates to a microcell module comprising a housing having mounted therein a plurality of microcell sub-bundles, wherein the housing comprises an interior volume bounded by respective end-plates, each end-plate having openings therein each of which is matably and sealingly engageable with a tubesheet of a corresponding sub-bundle, and wherein corresponding end-plate openings of the respective end-plates are in coaxial register with one another, such housing including a first end volume bounded by the end-plate at one end of the housing, and a second end volume bounded by the end-plate at the other end of the housing, a feed tube arranged for delivery of feed to the sub-bundles, and an outlet for discharging depleted feed from the interior volume, with such housing being selectively openable to expose an end-plate at at least one of the end volumes for accessing sub-bundles mounted in the end-plate for removal thereof and installation of a replacement sub-bundle, wherein the sub-bundles in the housing are series connected with one another and connected to a terminal leak-tightly extending exteriorly of the housing.
In a still further aspect, the invention relates to a method of making an electrochemical cell device, comprising:
forming a layer structure of sheets including a first sheet of fibrous microcell elements arranged in parallel side-by-side arrangement as a first sheet, and a second sheet comprising a parallelly aligned spaced-apart arrangement of external current collector elements in a second sheet;
mating the first and second sheets in longitudinally off-set relationship to one another, so that said external current collectors extend beyond an edge of the first sheet, and internal current collectors of the fibrous microcell elements extend beyond an opposite edge of the second sheet;
adding corresponding layers of corresponding first and second sheets to the initial layer of first and second sheets, and disposing a porous insulative sheet between each of the respective layers, to form a multilayer structure;
shaping the multilayer structure into a predetermined sub-bundle shape, and potting same to impart a permanent shape thereto, wherein the permanent shape provides localized conformations of internal and external current collectors;
fabricating a plurality of sub-bundles in corresponding manner;
connecting the sub-bundles in sequence to form a series arrangement of sub-bundles; and
shaping the series-connected sub-bundles to form a bundle assembly.
A further aspect of the invention relates to a method of fabricating a microcell assembly, comprising:
forming a first layer including a first microcell sheet member comprising a plurality of fibrous microcell elements parallelly arranged and interconnected in a substantially planar conformation, with inner current collectors of the fibrous microcell elements axially extending from a first edge of a first sheet member, and a second sheet member of external current collectors overlying the first sheet member, positioning each current collector in contact with at least one microcell fiber of the first sheet member and extending beyond an opposite, second edge of the first sheet member;
disposing an insulating sheet on said first layer;
forming a second layer including a first microcell sheet member comprising a plurality of fibrous microcell elements parallelly arranged and interconnected in a substantially planar conformation, with inner current collectors of said fibrous microcell elements axially extending from a first edge of a first sheet member, and a second sheet member of external current collectors overlying the first sheet member, positioning each current collector in contact with at least one microcell fiber of the first sheet member and extending beyond an opposite, second edge of the first sheet member; and
electrically connecting the inner current collectors of the first layer with the outer current collectors of the second layer to form a series connection therewith.
A still further aspect of the invention relates to a method of fabricating a microcell module, comprising:
providing a gas feed chamber including a perforate plate member;
positioning on the perforated plate member a microcell assembly comprising a plurality of fibrous microcell elements and associated external current collectors defining a plurality of microcells, and potting the microcell assembly at respective ends thereof by potting members forming respective seal faces which when the seal faces at their periphery are abuttingly reposed in a housing, form a shell and tube structural arrangement, wherein the perforated plate member is intermediately positioned between the potting members.
In another aspect, the invention relates to a method of fabricating a microcell sub-bundle article, comprising:
forming a sheet assembly including a first microcell sheet member comprising a plurality of microcell fibers parallely arranged and interconnected in a substantially planar conformation, with inner current collectors of the microcell fibers axially extending from a first edge of a first sheet member, and a second sheet member of external current collectors overlying the first sheet member, with each current collector in contact with at least one microcell fiber of the first sheet member and extending beyond an opposite, second edge of the first sheet member; and
axially rolling the sheet assembly into a cylindrical pre-form, applying a porous and electrically insulative wrap to the outer cylindrical surface of the cylindrical pre-form; and potting respective ends of the cylindrical pre-form, to yield the sub-bundle,
wherein the first and second sheet members form a cell.
A further aspect of the invention relates to a method of fabricating a microcell article comprising a series of microcell sub-bundle articles, said method including fabricating a plurality of microcell sub-bundle articles having positive electrode and negative electrode structures, parallely aligning said sub-bundle articles with one another in side-by-side relationship of consecutive sub-bundle articles, thereby forming a bundle of said sub-bundle articles, and electrically interconnecting the sub-bundle articles in series.
Other aspects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.